Generally, the place at which the FATE LINE cuts HEAD LINE, that is 35th year of life. So, by measuring the length and taking the same ratio on your life line, you can know the age of anyone. Similarly, you can take same ratio on other lines of palm to know the age of happening of different events of life.
(It is to be noted that these prediction should not be accepted as final for determining anyone's age as some other astrological factors can affect this.)